Download Cosmology2 - NMSU Astronomy

WHAT KIND OF UNIVERSE DO YOU LIVE IN?
What is the fate of the Universe?
time
History of the Universe in a Nutshell
14 billion yrs
1 billion yrs
galaxies
form
380,000 yrs
atoms
form
3 min
time
nuclei
form
As the universe expanded it cooled and its density decreased
This is what drove all the physics: temperature and density
Today the universe is 2.73 degrees Kelvin (absolute)
Structure Formation (Galaxies)
Driven by gravity…
Dark matter is immune to temperature of
normal matter (doesn’t interact with light).
Dark matter has always been “cold” and so
contracted under gravity and thus provided
gravity seeds for overall structure growth.
Compare real (above) to model (left)
We used to teach 3 possible fates:
OPEN------ density < “critical”; forever expanding
FLAT------- density = “critical”; expanding, but forever slowing
CLOSED - density > “critical”; expanding, then contracting and collapse
All we had to do was determine what the density of the universe is compared
to the critical density!
Closed
Flat
Open
Angular variations in the temperature of the cosmic microwave background
provide clues to geometry of the universe.
Most angular variations are about 1 degree apart. They indicate that the universe
has a flat geometry…
The Universe is Flat!
If the universe is flat, then it has 100% of the critical density!
We would expect that normal matter comprises all the density, right?
Measurements of the abundance of deuterium and lithium (relative to hydrogen)
indicate that normal matter comprises only 4% of the critical density!
How can this be?
The universe has critical density,
but matter is only 4%
What is the remaining 96% of the
density of the universe?
But, 90% of matter is actually dark matter!
In galaxies, the rotation
speeds indicate that 90% of
the matter is invisible, i.e.
dark matter.
In galaxy clusters, the
confined hot X-ray gas also
indicates that 90% of the
matter is invisible, i.e. dark.
Hmmm, that still accounts for only about 30% of the critical density!!!
Where is the additional 70% that is required for a flat “critical” universe?
And then… all hell broke loose with the supernovae distances...
Standard Candles: Supernovae
•
Surveys of SNe yielded a
surprising result: the peak
brightness of the SNe is lower
than predicted by Hubble’s law!
•
This means that the SNe are
farther away than if the
expansion rate of the universe
were just coasting and slowing
down under gravity…
•
Something is forcing space to
expand faster and faster with
time!
The expansion is not slowing down with time… it is accelerating!!!
Precision Cosmology?
In Einstein’s equations, there is an anti-gravity term called the cosmological constant; at
first Einstein thought it was a mistake… we now know it is a mysterious form of energy
density, we call it dark energy.
MATTER
DARK MATTER
DARK ENERGY
MATTER + DARK MATTER + DARK ENERGY = TOTAL
4%
+
33%
+
67%
= 100%
We know that the total matter/energy density is 100% of the critical value (the
universe is flat)… But, we know only what 4% of the total matter/energy density
is!!!!!
So, after the Big Bang, the universe decelerated as it expanded, and about 6
billion years ago it started accelerating as dark energy began to dominate
gravity
This may sound crazy!
But, X-ray observations of
galaxy clusters help
determine the distances to
the clusters.
The results indicate that
the universal expansion
was slowing down at times
further back than 6 billion
years ago.
So, yes
Deceleration…
Then…
Acceleration.
We now speculate that the universe will continue accelerating and, if dark
energy continues to grow in strength will end in what is called the Big Rip!
Big Rip?
Right? And what will we be saying in 10 years from now?
Whatever you do in this life….
Stay tuned to ASTRONOMY!
Good luck and best wishes for you endeavors!